So researchers in sunny Brazil investigated another cardio culprit: cholesterol. They tracked cholesterol levels in a quarter million people living outside Sao Paulo—mostly middle-aged men and women. And they found that levels of LDL, or bad cholesterol, shot up during the South American winter. The change pushed 18,000 people with borderline cholesterol levels over the threshold. The finding was presented at a recent meeting of the American College of Cardiology. [Filipe Azevedo Moura et al., Seasonal variation of lipid profile and prevalence of dyslipidemia: a large population study]

Why the wintertime spike? People tend to exercise less in winter, and to eat more fatty foods. We also get less vitamin D from sunlight—and studies suggest vitamin D may improve the ratio of good to bad cholesterol.

The biggest concern, the researchers say, is that one annual cholesterol check could over or underestimate your actual levels—and have an outsized influence on whether or not your doctor prescribes meds. The study doctors offer their own wintertime prescription: exercise, eat healthy and get more sun. Might keep you young at heart.